The demand for higher performance semiconductor devices is continuing and has resulted in a continuing demand for improvements in the art of manufacturing semiconductor devices. One of the most important factors in increasing the performance of a semiconductor device is to increase the speed of the integrated circuits on the semiconductor device. Another of the most important factors in increasing the performance of a semiconductor device is to pack more and more electrical circuits onto a semiconductor device without increasing the size of the device. In order to include as many electrical circuits onto a device of a give size, it is necessary to design and manufacture the electrical circuits with increased density.
In order to manufacture the electrical circuits with increased density it is necessary to improve the projection optical systems used to accurately project the patterns on a reticle, also known as a mask, onto the surface of a substrate, such as a semiconductor wafer. As is known in the semiconductor manufacturing art, a semiconductor wafer is subjected to a multitude of processes. Also, as known in the semiconductor manufacturing art, the processes are not done in a single machine, which necessitates moving the partially completed semiconductor wafer from machine-to-machine. Certain of the machines have projection optical system to project the pattern on a reticle onto the wafer. The projection optical systems typically have differing aberrations and have differing degrees of correction for these aberrations. One such aberration is distortion that can have differing degrees of correction from machine-to-machine. Current projection optical systems only have the capability to adjust magnification of the image and to correct low order distortion. The current projection optical systems do not have any capability to adjust high order distortion including random component of distortion. As a result, a first pattern printed onto a semiconductor wafer in a first machine with a current projection optical system will have a certain amount of distortion in the printed pattern and a second pattern printed onto the semiconductor wafer in a second machine with a current projection optical system will have a certain amount of distortion in the printed pattern, which more than likely will not match the distortion in the first printed pattern. As the printed patterns have been printed closer and closer, a mismatch in distortion in the two machines can cause portions of the two separately printed patterns to not overlap as designed. This results in a failure of the semiconductor device.
Accordingly, there is a need for a projection optical system in which the distortion can be controlled to match the distortion in a previous machine.